The influence of needle eccentric motion on injection and spray characteristics of a two-layered eight-hole diesel injector

To meet the increasingly stringent emission regulations nowadays, the quality of injection and spray must be high. The eccentric displacement of an injector needle during injection influences fuel flow characteristics within the nozzle (in-nozzle) and the injection and spray characteristics from the nozzle holes. In this study, the effect of the needle (within a double-layered eight-hole nozzle) on in-nozzle flow, injection and spray was analyzed and characterized. The model was validated by comparing simulation and experimental results from each hole (hole-to-hole). The hole-to-hole internal flow characteristics, injection characteristics, and spray characteristics under various needle eccentricities and radial displacements (needle deflections) were also analyzed. From the results, different asymmetric fuel flow characteristics were noted. Nozzle holes close to the needle deflection formed spray jets with wider cone angles and shorter penetration whereas nozzle holes at the opposite side of the needle deflection, formed spray jets with relatively smaller cone angle and higher penetration. As the needle lift got closer to the maximum lift, the effect of the eccentricity on in-nozzle fuel flow decreased. The direction of the needle eccentricity (needle deflection) dictated the flow dynamics within the holes which then affected the type of cavitation. The holes closer to the needle developed string type cavitation due to the formation of vortex flow in the nozzle. The eccentric effect of the needle was felt more by the lower layer nozzle holes than the upper layer holes.